I imagine this question has been asked before, but I was unable to find it in my quick scan of the archives.

I'm taking an RTW in ten or so months, and will have a decent chunk of American miles by then. Given the open-jaw rules, the itinerary I do on OW will be <35k, and I should be able to afford either the 190k business or the 140k economy. Originally, I was planning to either buy one-ways (on no particular alliance) as I went or to one-way to Australia and buy a oneworld or Star RTW there.

Certainly, it would be optimal just to use a oneworld award, but is there any hope of actually being able to book one? The flights would all need to be within a week or so of my projected date, and there are over a dozen (spread out over 9 months). If it is bookable, when would be the latest one would want to book one? The flights would be along the lines of (somewhere in USA)-SYD-AYQ-BNE-NRT-PEK-HKG-JNB-Europe-CCS-USA, beginning Aug 08.

Worth saving up those miles, or should I just plan on buying the flights?

If you haven't done so already, check out the rules in the " oneworld awards using American Airlines miles" sticky. There's immense flexibility on routing derived from this:

If you don't mind and have time for odd routing if needed then I imagine you'll be able to make a booking given your +/- a few days flexibility. I worry about your HKG-JNB somewhat though - others will know better but the indiret route is very indirect (via bcn, mad or lhr) When will you have enough miles?

This will be a bit of a challenge, because the ticket is valid for 1 year from date of issue yet must be issued no later than 14 days after booking, meaning the earliest you could book is around 3 months before departure; at that time it's not going to be easy to find decent award seats to SYD.

Ah, I'd missed this "The ticket is valid for one year from the date of issuance (not from the date of the first flight).". Makes life trickier!

You have a couple of segments that are difficult to get award seats on so I would not hold out much hope.

milliomiler...which in particular? I understand US-SYD is difficult, but is this true even, say, via HKG or NRT?

So a few hours on Qantas' tool, and I think this route might be doable after all. Optimal for me is SFO-SYD-AYQ-CNS-SYD-NRT-HKG-DEL-HKG-LHR-JNB-LHR-AMM-MAD-EZE-SCL-LPB, with the second SYD and both LHRs not being stopovers. Total mileage is ballpark 40k. Pretending that I'm booking two months out, I found flights only a day or so off for the segments up to Narita, the HKG-JNB flight and the MAD-EZE segment. The other flights would be on Cathay or LAN, and Qantas' tool does not allow me to select a number of cities in the list (say, Delhi) for some reason, so I can't quickly check these. Are these airlines simply not loaded? (Perhaps it's time for me to pony up for expertflyer...) The only flights that came up on any search were JL/QF codeshares, BA, QF and AA. This would be a great booking as I would save almost $3000 all told on my flights for this trip. I checked everything in coach as business awards were nigh impossible on a lot of these flights.

QF online award search is limited to 200 odd destinations (all QFs + a semi-random assortment of other OW destinations). Last I spoke with QF about it they had no plans to add more destinations online

Not for awards, an area where EF is severely limited.